Rewinding machine and winding method

ABSTRACT

The rewinding machine includes a weakening device for weakening the web material along a substantially transverse weakening line, along which the web material is severed at the end of the winding of a log. The weakening device is controlled so as to generate the weakening line in a manner synchronized with the completion of winding of the log.

TECHNICAL FIELD

The present invention relates to a winding or rewinding machine for forming rolls of web material. According to another aspect the invention relates to a method for winding a web material in rolls.

STATE OF THE ART

In numerous industrial fields, and in particular in the field of paper converting—especially converting of tissue paper for producing rolls of toilet paper, rolls of kitchen towels and the like—so called rewinding machines are used that, starting from one or more paper material reels of large diameter, form individual logs of axial dimension equal to the width of the web material, typically 2-5 m, and of diameter equal to the diameter of the rolls destined for the final consumption. The logs produced by the rewinding machine are subsequently cut into a plurality of rolls of the desired axial length.

In the modern rewinding machines, winding is carry out through a so called peripheral or surface system, wherein the log being formed is maintained in a winding cradle formed by a plurality of rollers rotating in a concordant direction and in surface contact with the log being formed so as to transmit the winding motion. In other older rewinding machines winding is carried out in a cradle, in which the log is maintained on a winding spindle, to which the rotation movement is imparted. There are also machines combining a peripheral winding system with spindles or tail chucks for supporting and controlling the log being formed.

In general, the rewinding machines have members for interrupting the web material, which is fed continuously by the reels present in the unwinders, at the end of winding of each individual log. These severing members are synchronized with the means or devices that start winding of the subsequent log.

In some rewinding machines winding is carried out around tubular winding cores mounted on winding spindles. The tubular cores are usually made of plastic, paper or cardboard, and they remain inside the log after winding. In other rewinding machines the winding spindle is extracted so as to obtain a log provided with a central hole, but devoid of winding cores. In further types of rewinding machines winding is carried out without a winding spindle, by simply winding the web material around itself, starting from a central nucleus and forming around this latter the finished log.

Independently of the type of used rewinding machine, the start of the winding of each individual log is one of the critical aspects during the winding phases. When winding is carried out around tubular cores, one of the critical aspects is represented by the transport of the leading end, formed by cutting or severing the web material, to the new core and by the start of the winding of the first turns. Different systems have been designed to perform the operations of severing the web material, transporting and anchoring the winding cores. U.S. Pat. No. 6,648,266 and U.S. Pat. No. 5,979,818 disclose a particularly efficient rewinding machine, wherein the web material is severed by means of a rotating member which pinches the web material against a movable surface, for example against the surface of the main winding roller of a winding cradle of the peripheral type. The winding core, is provided with a glue to anchor the leading edge generated by severing and to start in this way the winding of the subsequent log. The severing member acts on the web material in a position intermediate between the log which has been just wound and the new winding core inserted in the machine.

Rewinding machines produced according to this principle are extremely efficient and allow to achieve high winding speeds thanks to the efficient control on the free end of the web material after it has been severed. However, due to the way in which the web severing system is designed, the logs are formed around the winding cores with a head portion forming, inside each log, a fold of particularly great length. This entails irregularities in the first winding turns and a quality of the finished product not equal to that which can be obtained through other slower winding systems. Furthermore, as the severing member acts between the log, wound during the winding cycle which is ending, and the new core which is being inserted, it is necessary to have a particularly long rolling surface, and therefore a particularly long insertion channel.

Other rewinding machines having web material severing systems arranged upstream of the area of insertion of the winding cores are disclosed in EP1525148.

WO 2007/081244 discloses a perforating device that can be used in a rewinding machine, wherein on the toothed blades of the perforator a colored liquid is applied. This known device has the function of coloring the perforation lines that separate each of the various sheets of a roll in tissue paper by means of the liquid.

SUMMARY OF THE INVENTION

According to one aspect, an object of the present invention is to provide a rewinding machine that completely or partially overcomes at least one of the problems of the known rewinding machines. According to another aspect, a further object of the present invention is to provide a winding method using a rewinding machine, preferably of the peripheral type, wherein one or more of the problems of the traditional methods are completely or partially overcome.

Substantially, the invention is based upon the concept of interrupting, severing, or cutting, the web material in two phases. In a first phase the web material is weakened at a line, along which severing of the web material is subsequently completed, thus forming the tail end of the log, the winding of which is being completed, and the leading end destined to form the subsequent log.

According to one embodiment, the present invention provides a rewinding machine comprising: a web material feed path; a winding cradle, preferably of the peripheral type; severing members for interrupting the web material at the end of winding of each log; a weakening device for weakening the web material along a substantially transverse severing or weakening line, in correspondence of which the web material is severed at the end of winding of a log. The weakening device is controlled so as to generate the weakening line synchronized with the completion of winding of the log.

In some embodiments the rewinding machine according to the present invention provides an inserter for winding cores or spindles, to produce log of web material wound about tubular winding cores or spindles. Preferably, but not necessary, the tubular cores are destined to remain inside the log. In some cases, they are provided with a glue, applied for example along one or two rows having a continuous or discontinuous development in the substantially longitudinal direction of the tubular core, for the purposes that will be described in greater detail hereunder.

By means of a rewinding machine of this type it is possible to weaken the web material in an adequate position along the path of the web material upstream of the area in which it will be definitely severed to form the leading and tail ends during the exchange phase, i.e. during the phase in which the finished log is separated from the web material and unloaded from the machine and the new log starts winding.

Through a weakening line of this type it is possible to maintain the control on the web material fed along the feed path across the machine, from the position in which the weakening member or device is arranged and the position, preferably downstream (according to the direction of feed of the web material) of the area of insertion of the winding core, without the need for using vacuum members or other complex retaining systems for retaining the leading end of the web material. Moreover, the weakening of the web material upstream of the area of insertion of the winding core allows to obtain the subsequent complete severing of the web material with a particularly simple system, for example with a very limited acceleration of one of the winding rollers forming the winding cradle. This can be obtained thanks to the fact that the web material has been previously weakened along the weakening line during the first phase of the operations for severing the material.

In some embodiments, when a winding core is used, provided with a glue to transfer on the core itself the free leading end of the web material, severing of the web material can be completed simply due to the effect of the adhesion between the web material and the core by means of the glue applied on the core. In this case the severing members for interrupting the web material are represented by the same core inserter which is synchronized with the position of the weakening line generated on the web material.

According to a different aspect the invention relates to a method for winding logs of web material about winding cores, wherein: at the end of winding of a log, in a weakening position arranged along the feed path of the web material upstream of the severing position, a weakening line is formed on the web material; the web material is fed along the feed path, bringing said weakening line towards the severing position, and is severed in said severing position.

In some embodiments it is provided for the web material to be weakened by applying a liquid, preferably a water based liquid, in correspondence of said weakening line.

Further advantageous features and embodiments of the rewinding machine and of the method according to the present invention are indicated in the appended claims and shall be described hereunder with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by following the description below and the attached drawing, which shows a non-limiting practical embodiment of the present invention. More particularly, in the drawing:

FIGS. 1A to 1F show a schematic side view of a rewinding machine according to a first embodiment of the present invention, in a winding operative sequence;

FIGS. 1G to 1I schematically show the formation of the weakening line and the subsequent tearing or severing of the web material along said line;

FIG. 2 shows a schematic side view of a rewinding machine according to the present invention in a further embodiment;

FIG. 3 shows a schematic side view of a rewinding machine according to a further embodiment of the present invention;

FIG. 4 shows a partial schematic side view of a rewinding machine in a modified embodiment;

FIG. 5 shows a schematic enlargement of the surface of the main winding roller of the rewinding machine in an improved embodiment; and

FIGS. 6A to 6D show an operative sequence of a further embodiment of a rewinding machine according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

With initial reference to FIGS. 1A to 1F, in one embodiment the rewinding machine 1 comprises a winding cradle with a first winding roller 3, a second winding roller 5 and a third winding roller 7. Between the rollers 3 and 5 a nip 9 is defined, through which the web material N passes, fed along a winding path described in greater detail hereunder and developing around the first winding roller 3. The winding roller 7 is provided with a movement for moving towards and away from the winding rollers 3 and 5, so that the three rollers 3, 5, 7 form a winding cradle of variable dimension to allow the increase of the diameter of each log R formed inside the cradle.

In some embodiments the rewinding machine 1 has a perforating unit 11 (FIG. 11A) to generate perforating and severing lines on the web material N at regular intervals, so as to subdivide the web material N into individual small sheets, which can be separated from each other for the use. The perforating unit 11 is known per se and will not be described in greater detail hereunder. In other not shown embodiments the perforating unit 11 can be controlled so as to generate an individual perforating line, or it can be completely omitted, for example for producing logs R with a greater diameter destined to the industrial use instead of the domestic use.

The path of the web material N develops through the perforating unit 11 (if present) and around a guide roller 13 arranged nearly close to the winding roller 3, around which the path of the web material N continues to develop until it achieves and crosses the nip 9 between the winding rollers 3 and 5 and then enters into the winding cradle in order to wind around the winding core A and form the log R.

The above described structure is a typical structure of a so called surface or peripheral rewinding machine, wherein the log R is formed by maintaining it in rotation by contact between the rollers 3, 5, and 7. Also different conformations can be provided for the winding cradle and/or the presence of tail chucks for supporting and controlling the winding cores in at least some of the phases of formation of a log, as it is well known to those skilled in the art.

According to some embodiments, around the winding roller 3 a rolling surface 15 develops, defining a channel 17 between the surface 15 and the cylindrical surface of the winding roller 3. The winding cores A are sequentially inserted, in the manner described below, inside the channel 17 so as to start the cycle of winding of each log.

The rewinding machine 1 comprises a weakening device 21 arranged, designed and controlled so as to weaken the web material N in correspondence of a weakening line, along which the web material N will be subsequently severed to form the tail end of the log R and the head end from which the winding of the subsequent log will start.

In some embodiments, the weakening device 21 comprises an element 23 that rotates in a controlled manner around an axis of rotation 23A substantially parallel to the axis of rotation of the rollers 3, 5, 7, and 13.

In some embodiments, as shown in the drawing, the weakening device 21 is designed so as to apply a liquid, preferably for example a water-based liquid, on the web material N along a substantially transverse line. In some embodiments the liquid can be simply water, although other embodiments would be possible, for example the application of a colored liquid when one desires for example optically to mark the position of the severing line of the web material. In other embodiments the liquid applied by the weakening device 21 can be constituted by or can contain an adhesive or glue, so that following the complete severing of the web material the free tail end can automatically adhere to the formed log R and/or the head end can automatically adhere to the new winding core without the need for further glue.

In the illustrated embodiment the dispensing member comprises at least one rotating element 23, which at its distal end is provided with a pad 25 which is wet with water or other suitable liquid to be applied to the web material N. In order to wet the pad 25 it is possible for example to provide the rotating element 23 with a movement of immersion inside a tank 27 containing the liquid, which is generically indicated with L. In this way the rotating element 23 can immerse the pad 25 inside the tank 27 in order to wet it. The extraction movement for extracting the pad 25 from the tank 27 allows the subsequent application of the liquid on the web material as described in greater detail hereunder.

In other embodiments, as illustrated in the drawing, the pad 25 is wet with the liquid L by a movable member 20 which is completely or partially housed inside the tank 27 and provided with an alternate immersion and emersion motion according to the double arrow f29. In this way it is possible to maintain the rotating element 23 with its pad 25 completely outside the tank 27, avoiding the movement of the element 23 for immersing the pad 25 in the liquid L contained inside the tank. In this case the member 29 transfers the liquid from the inside of the tank 27 to the pad 25 every time it is necessary, for example for each winding cycle, i.e. each time that an individual log R is wound. Alternatively, guns or nozzles in series can be provided, instead of the member 29, for wetting the pad 25.

In the illustrated embodiment the logs R are wound around substantially circular winding cores A, for example cores made of cardboard, plastic, paper or the like. According to the illustrated embodiment, a glue is applied on the winding cores A. The glue is preferably applied according to two nearly longitudinal lines, i.e. substantially parallel to the axis of the winding cores A or, anyway, extending along the length or at least a great part of the length of the winding cores A. The lines of glue can be continuous or discontinuous, can be formed by individual areas of different shape, provided that they are arranged with a frequency and a distance from each other sufficient to guarantee the anchoring of the free leading end formed by the web material N following the severing thereof, as described hereunder.

In the embodiment illustrated in FIGS. 1A to 1F, a first glue dispenser 31 and a second glue dispenser 33 are provided, to apply two continuous or discontinuous lines of glue in angularly staggered positions on each individual winding core A. In the illustrated embodiment the dispensing members 31 and 33 are substantially identical, but it is also possible to use dispensers that are different from each other, or dispensing members with a shape different from that illustrated. In some embodiments each dispenser 31, 33 has a tank 31A and 33A respectively, inside which a first glue C1 and a second glue C2 respectively are contained. Inside each tank a movable member 31B and 33B can be immersed. The movable members 31B and 33B are provided with an oscillating movement according to the double arrow indicated in the drawing so as to be immersed in the glue C1 or C2 and emerge from it until they touch each core A to be glued along a nearly longitudinal line. In this way, on the individual cores A two lines of glue are applied that are angularly staggered for the purposes describe below.

It is also possible to use movable members for lifting the glue from the individual tanks 31A, 33A with different shapes but having substantially the same function as the members 31B, 33B. For example, a thread can be provided, movable along a closed path defined for example between two pulleys. The upper segment of the thread is arranged at an area of application of the glue to the cores A, corresponding to the position taken by the movable members 31B, 33B when they are lifted, and a lower segment immersed in the glue C1, C2, for example in a position corresponding to that taken by the members 31B, 33B when they are immersed in the glue.

To the glue dispenser 31 a first transferring unit 35 is associated, which picks up individual cores A from a storage device 37 and transfers them individually, after they have individually received a first line of glue, to a second transferring unit 39 associated to the second glue dispensing member 33. The transferring member 39 then transfers the cores towards the entrance of the channel 17, into which the cores are inserted to start the cycle of winding each individual log R according to the method described below.

FIG. 1A shows an intermediate phase of the winding cycle of a log R which is in the winding cradle 3, 5, 7. The transferring member 35 has engaged a new core A, which is receiving a first line of glue RC1 through the movable member 31B of the glue dispenser 31. The second transferring unit 39 is in a waiting position and the movable member 33B of the second glue dispenser 33 is immersed in the glue C2. The rotating element 23 of the weakening device 21 is in contact with the movable member 29 to receive the liquid L on its pad 25.

In FIG. 1B the core, previously engaged by the transferring unit 31, has been transferred by it to the transferring unit 39, which maintains it in correspondence of the second glue dispenser 33, so as to apply on the core a second line of glue RC2, angularly staggered relative to the line of glue RC1. The log R in the winding cradle 3, 5, 7 has substantially achieved its final dimension, determined for example by the length of the wound web material. The rotating element 23 of the weakening device 21 is still in a waiting position.

FIG. 1C shows the phase wherein the weakening device 21 applies a line of liquid L, which forms the weakening line that, in this embodiment, matches one of the perforation lines generated by the perforating unit 11. The second transferring unit 39 is transferring a new core, provided with the two lines of glue RC1 and RC2, to the entrance of the channel 17.

In FIG. 1D the new core has been inserted into the channel 17 and it is rolling along the rolling surface 15 towards the nip 9, whilst the rotating element 23 of the weakening device 21 is returned in its waiting position of FIG. 1A. Actually, the rotating element 23 of the weakening device 21 is actuated and performs a rotation by 360° only once per winding cycle, i.e. for each cycle of formation of a single log R. It is accelerated until it achieves with its pad 25 a peripheral velocity substantially equal to the feeding speed of the web material N along the feed path thereof, i.e. a peripheral speed substantially corresponding to that of the winding roller 3, around which the web material N is driven and guided and which supports the web material N when it is touched by the pad 25 to receive the liquid L.

The web material, wet along the weakening line with the liquid L, continues to adhere to the winding roller 3, even if greatly weakened, due to the liquid impregnating the cellulosic fibers of which the web material N (typically tissue paper) is made. In this way control of the web material N is maintained, which is not completely severed following the weakening caused by the liquid applied by the pad 25. The control of the web material is further improved thanks to the fact that the liquid L, which has impregnated the web material N along the weakening line, tends to make the web material to adhere to the winding roller 3. This latter can be coated, partially or completely, for example along annular areas, with a material with a high friction coefficient, so called “grip” material, which assures a further control on the web material N and the transferring thereof along the feed path around the winding roller 3.

In FIG. 1D the weakening line indicated with I is in a position which is at least approximately phased with the position of the new core A provided with the lines of glue RC1 and RC2 that is rolling inside the channel 17. In the instant represented in FIG. 1D the weakening line is upwards, i.e. before the core A relative to the direction of feed of the web material N. As the axis of the core A moves at a speed equal to the half of the speed of feed VN of the web material, whilst the weakening line I obviously moves with a speed VN, said weakening line I will pass the winding core A, as shown in the subsequent phase represented in FIG. 1E. Here the interruption line I is downstream (relative to the direction of feed of the web material N) of to the new core A that continues to roll on the surface 15 along the channel 17 towards the nip 9. By moving from the position of FIG. 1D to the position of FIG. 1E the core A has transferred the glue C2, applied by the second dispenser 33, to the area of the web material N adjacent to the severing weakening line I towards the log R. In this way, when the web material N will be interrupted along the line I, the glue C2 will close the free tail end of the web material forming the log R.

In the phase illustrated in FIG. 1E the line of glue RC1 is in contact with the web material N due to the effect of the rolling of the core A along the surface 15. In this way, also thanks to the light pressure exerted between the core A and the roller 3 (due to the fact that the channel 17 has a dimension slightly lower than the diameter of the core A, which slightly deforms so as to advance along said channel) the web material N is made to adhere to the core A in correspondence of the line RC1 of glue. The adhesion effect obtained, thanks to the glue C1, between the web material N and the new core A, which continues to roll moving forward along the channel 17, is sufficient to cause the breakage of the web material along the weakening line I.

In fact, along this weakening line the web material, soaked with liquid, has a very low tensile strength and substantially looses its elasticity. The slight traction, to which the web material N is subjected due to the effect of the relative movement between the core A rolling on the surface 15 and the web material N tending to rotate with the roller 3, causes tearing, i.e. complete severing of the web material along the weakening line I. Tearing practically occurs thanks to the fact that the trajectory of the web material is altered by the presence of the winding core. When the web material adheres to the core, and this latter rolls in the introduction channel, the web material is forced to leave its original trajectory (along the surface of the winding roller 3) and starts to follow the surface of the winding core.

What is obtained is represented in FIG. 1F: the severing position of the web material N is defined in an intermediate position between the core A and the log R, with formation of the tail end LC that, thanks to the glue C2, will adhere to the log R. The interruption of the web material in the severing position between the core A and the log R also causes the formation of the head end LT that adheres to the core A, which, continuing to roll on the surface 15 towards the nip 9 and thus entering into contact firstly with the second winding roller 5 and subsequently with the third winding roller 7, by continuing to rotate will cause the formation of the new log R repeating the winding cycle and the subsequent exchange cycle described above with reference to the sequence of FIGS. 1A-1F.

For a better understanding of the mechanism for weakening and subsequently severing the web material, FIGS. 1G to 1I schematically show a plan portion of a web material N, on which are represented the perforation lines P1, P2, P3, the weakening line I and the severing line of the web material, generated as disclosed above, with formation of the ends LC and LT.

More in particular, FIG. 1G shows a plan portion of web material N winding on the log R. P3 indicates the perforating line, in correspondence of which the liquid is applied to weaken the web material forming the weakening line I, whilst P1 and P2 indicate other perforating lines generated by the perforating unit 11. In the subsequent FIGS. 1H and 1I it can be observed how the weakening line moves towards the log winding area and then, in correspondence of said area, the separation occurs generating the leading end LT and tail end LC.

In view of what has, been described and illustrated above, it should be understood that with the rewinding machine according to the present invention the operation of severing the web material is substantially subdivided into two phases: in a first phase the weakening is performed along the line I of the web material by means of the device 21. In a second phase the interruption is accomplished, i.e. it is completed forming the leading and tail ends LT, LC, exerting a very modest mechanical action sufficient to overcome the remaining resistance of the cellulosic fibers of the web material N in correspondence of the weakening line I. As indicated above, this interruption is also obtained simply due to the effect of the traction exerted on the web material N by the glue, which makes the head end LT to adhere on the new core A inserted in the machine. In this way it is not necessary to have expensive additional members for cutting or severing the web material. The whole rolling channel 17 remains devoid of mechanical members and the portion of web material between the leading end LT and the adhesion or anchoring point in correspondence of the line of glue RC1 is extremely short, thus obtaining a very regular winding without creases also of the first part of web material N of each log R.

FIG. 2 shows a modified embodiment of the rewinding machine according to the present invention. The same numbers indicate same parts as, or equivalent parts to, those of the embodiment shown in FIGS. 1A to 1F.

In this embodiment the weakening device 21 comprises again a rotating element 23, which, however, does not receive the liquid L from a tank, but projects it through a nozzle carried at the distal end of the rotating element 23, so as to form an adequately shaped jet G of liquid, or a plurality of jets arranged side by side. These jets wet the web material N, thus forming the weakening line I. In order to obtain an easier synchronization and to avoid that the weakening line I is produced with an excessive dimension in the direction of the longitudinal development of the web material, to the rotating element 23 screens 24A, 24B can be associated, between which a slot is defined, developing nearly parallel to the axis of the winding roller 3. In this way the jet or jets G of liquid L generated by the nozzles carried by the rotating element 23 wet an area I of very limited dimensions.

FIG. 4 shows a rewinding machine according to the present invention in a further modified embodiment. The same numbers indicate parts identical or equivalent to those in FIGS. 1A to 1F. In this embodiment the pad 25 is wet through contact with a distributor comprising a rotating roller 30, whose surface is continuously wet by means of a dispenser 32. The surface of the rotating roller 30 can be machined, for example to provide a series of micro-cavities, so as to hold the water or other liquid to be transferred to the pad 25.

Even if the weakening obtained through the application of a liquids is particularly advantageous as, among other things, it allows to maintain a better control of the web material that thanks to the liquid tends to adhere to the roller 3 in a manner sufficient not to detach due to the effect of the ventilation caused by the rotation of the roller 3, in other embodiments the weakening line can be generated mechanically or pneumatically. At this end nozzles can be provided inside the winding roller 3, which generate air flows in an angularly preset position in correspondence of the weakening line I. Alternatively, the air flows can be generated by an external system, similar to that represented by the element 23 in FIG. 2. In other further embodiments the weakening device can be of the mechanical type. FIG. 3 shows a schematic embodiment, wherein a mechanical arrangement is adopted for generating the weakening line. In this figure again, parts equal or equivalent to that of the previous embodiments are indicated by the same reference numbers. In this embodiment the severing device 21 comprises a rotating element 23, at the end of which a toothed blade or some other element is applied, which can perform a partial cut in cross direction of the web material N. The blade, indicated with 23X, cooperates with a counter-blade 26 associated to the winding roller 3. In some embodiments the counter-blade 26 can be arranged in a fixed position relative to the winding roller 3, and it can be therefore integral with the winding roller 3. This arrangement, however, has the great disadvantage of lacking flexibility in the operation of the machine, in particular as the position, in which the weakening line is formed, is constrained and it cannot be changed at will, as the counter-blade 26 is an integral part of the roller 3 and rotates together therewith.

In a different embodiment, shown in FIG. 3, the counter-blade 26 is carried by a flexible member 28 driven around the winding roller 3 and a further roller or series of pulleys 28X. The flexible member can move independently of the winding roller 3, being formed for example by a plurality of belts driven around guide pulleys coaxial to the roller 3, this latter being formed by a plurality of axially aligned sections. Such a configuration is known for other purposes and it is described for example in WO-A-2008/050370, to which reference should be made for greater construction details. In this way the counter-blade 26 can be brought in an active position opposite to the rotating element 23 only when it is necessary, i.e. during the exchange phase. As the counter-blade 26 is in this case provided with a movement which is independent of the rotation movement of the winding roller 3, it can be positioned in any instance in the working position and cooperate with the blade 23X of the weakening device 21 in any desired instant during the winding cycle. In this way a flexible machine is obtained, wherein the length of each log R can be chosen at will without constraints relative to the diameter of the winding roller 3.

Both in the configuration of FIG. 3 and in the configuration of FIG. 2 the principle remains valid of severing the web material in two phases: a first weakening phase with formation of the weakening line I and a second phase of complete severing, between the two phases the web material N being controlled and transferred around the roller 3 from the position (defined by the weakening device 21), in which the weakening line I is generated, and the severing position, in which the leading end LT is completely separated from the tail end LC.

The glue C1 for anchoring the leading end of the web material on the new core A is usually a more sticky glue, i.e. a glue harder than the glue C2, with which the tail end LC is anchored to the log R in order to seal it. In other embodiments the tail end LC can be closed by the adhesion effect given by the same liquid L applied by the weakening device 21, for example providing that the liquid L is a water solution also with high dispersion of an adhesive or glue. The quantity of glue in the liquid L and the quantity of liquid L applied to the web material N will be determined in such a manner as to avoid dirtying of the winding roller 3.

The use of a glue on the winding core, in order to make the leading end of the web material N adhere on the winding core following severing, is particularly advantageous as in this way there is no need for additional members for cutting or severing or tearing the web material: the weakening along the line I is sufficient to cause tearing of the web material due to the retention effect of the glue C1 on the core A.

Moreover, the concept upon which the invention is based can be implemented, although with lesser advantages, also in machines wherein a glue is not used, or wherein the glue is not sufficient to obtain tearing or complete interruption of the web material following the weakening thereof. For example, the web material can start the winding around the tubular core A due to the effect of electrostatic adhesion, through air flows or in any other manner, avoiding the application of glue on the winding cores. This is particularly useful when the winding cores are subsequently extracted from the log, which in this case will be a coreless log. In these cases, and also when the used glue has not sufficient adhesive power to cause the tearing of the web material weakened along the weakening line I, severing of the web material can be obtained in other manner.

In some embodiments interruption can be obtained for example by temporarily accelerating the upper winding roller 7, so as to cause a tension in the web material. This tearing system is already used in prior art machines. It however has the disadvantage that the high resistance and elasticity of the paper requires great accelerations of the movable winding roller. In fact, it is necessary to tension the paper or other web material N, with very modest accelerations, beyond the breakage limit thereof in order to obtain tearing along the weakening line, for example along a perforation line. In absence of other measures, also due to the elasticity that these materials (typically tissue paper) present, it is necessary to use very powerful and over dimensioned motors, able to accelerate in a very sudden manner to control the rotation movement of the winding roller 7.

By using the concept upon which the present invention is based, the previous weakening of the web material along a weakening line, along which the severing will be subsequently performed, allows on one hand to maintain the control of the web material N until the weakening line I is brought downstream (relative to the direction of feed of the material N) relative to the new winding core, and at the same time to obtain the tearing or severing of the material with much more modest accelerations of the winding roller 7, independently of the presence of the line of glue on the core. Furthermore, a high accurateness is not necessary in the position of the weakening line relative to the moment in which the roller 7 is accelerated.

In other embodiments, severing can be for example obtained by means of air flows generated by nozzles arranged in annular grooves of the winding roller 3 or housed inside this latter, which, in this case, can be provided with a series of perforations, through which the pressurized air flows pass, which cause tearing of the web material. In this case again the weakening made by the device 21 eases and facilitates tearing, which can occur with much more modest air pressures and therefore with advantages in terms of energy and of reduction of noise during operation of the machine.

In some embodiments, the winding roller 3, around which the web material N is driven and with which the web material remains into contact after it has been wet, can be processed so as to avoid that the web material N (generally constituted by tissue paper with one or more plies) remains adhering to the roller due to the effect of moistening. FIG. 5 schematically shows an enlargement of a portion of the surface of the roller 3 in a configuration in which the roller is knurled, i.e. it is worked to form engraving or cavities I and protuberances P which reduce the contact surface with the web material N.

In other embodiments a system can be provided for facilitating the detachment of the web material N from the roller 3 and/or facilitating the start of the winding of the web material N around the winding core A. FIGS. 6A to 6D show an operative sequence of an improved rewinding machine, wherein an auxiliary system is provided for detaching the web material N from the roller 3. The same numbers indicate the same or equivalent parts to those of the previous embodiments, which will be not described in detail. In this embodiment the machine has only one glue dispenser 33, which applies only one line of glue RC2 on the tubular cores A. To the glue dispenser 33 a transferring device 39 is associated, which sequentially inserts the cores A in the channel defined between the rolling surface 15 and the outer cylindrical surface of the roller 3.

In this embodiment the roller 3 has a cylindrical shell perforated with holes 3F, preferably distributed along the whole circumferential development of the roller. Inside the roller 3 a casing 3C is provided, inside which pressurized air is inserted and from which the pressurized air exits towards the inner cylindrical surface 3S of the roller 3. In this way it is possible to generate an air flow through the holes 3F of the roller 3. The angular position of the casing 3C, and consequently the angular position f the air flow, can be changed or adjusted according to the requirements and the conditions of operation.

Downstream of the area where air is blown from the roller 3, and upstream of the nip 9 between the winding rollers 3 and 5, an oscillating member 6 is arranged, hinged around ax axis 61A of oscillation and carrying, at its end, a plurality of nozzles 63 for blowing air, aligned according to a cross direction, i.e. orthogonally to the plan of the figure.

The operation of this machine is clearly illustrated by the sequence of FIGS. 6A to 6D. The core inserter 39 picks up a core A from the glue dispenser 33, which has already applied a line of glue RC2 on the core A in such a position that the glue is transferred on the free tail end of the log R under forming in the rewinding machine. The core picked up by the inserter 39 is inserted in the channel 17 (FIG. 6B), coming into contact with the rolling surface 15 and with the web material N driven around the roller 3. The core starts to roll until the glue line RC2 comes into contact with the web material N and at least a part of the glue is transferred to it. The synchronization is such that the glue is transferred to the web material in the area directly downstream of the weakening line I generated by the device 23, 25, preferably at a perforation line, as described above. The core A continues to roll towards the area where the blowing casing 3C is arranged. The operation is synchronized in such a manner that when the core is near the blowing casing 3C, the weakening line I is nearly in front of the casing 3C. In this phase an air flow is generated, which causes the tearing of the web material N along the weakening line I and the detachment thereof from the surface of the winding roller 3 (FIG. 6C). The air flow tends also to push the initial free end LI, which has been therefore formed, towards the new core A. The humidity absorbed by the web material in correspondence of the initial free end LI can be sufficient to obtain the adhesion of the material N to the new core and therefore the start of the winding. In order to increase this adhesion effect the weakening line can be formed using glue added to the water. The core, continuing to roll towards the nip 9, starts to be wrapped in the web material so as to start the new winding cycle. Preferably, as illustrated herein, the air flow is actuated only after that the core A pinched the web material N against the winding roller 3, so as to avoid a premature detachment of the web material N from the roller 3 or for a excessively long segment.

When the core A passes in the area where the device 61 is arranged, and overtakes it, this latter is made to oscillate in clockwise direction so as to generate an air flow through the nozzles 63, which facilitates the winding of the first turn of web material, in addition to the mechanical effect due to the rotation of the device 61 (FIG. 6D).

In some embodiments the device 61 can be omitted. In other embodiments, it can be replaced for example with a system of fixed nozzles, for example arranged with different angulations, and actuated sequentially so as to direct towards the initial free end LI an air flow oriented so as to facilitate the winding of the first turn of web material.

In some embodiments the system for blowing air from the inside toward the outside of the roller 3 can be combined with a system for applying double glue, as provided in the embodiments previously described, to apply glue both to the final end and to the initial end of the web.

It is also possible to omit the gluing of the core A completely, and to glue the final tail end LC outside of the rewinding machine with a sealer of the traditional type, whilst the adhesion of the initial free end LI on the core A is assured by the liquid applied along the weakening line I.

It is understood that the drawing only shows an example provided by way of a practical arrangement of the present invention, which can vary in forms and arrangements without however departing from the scope of the concept underlying the invention. Any reference numbers in the appended claims are provided for the sole purpose of facilitating reading of the claims in the light of the description and the drawing, and do not in any manner limit the scope of protection represented by the claims. 

1-26. (canceled)
 27. Rewinding machine for producing logs of web material, comprising a feed path of a web material, a winding cradle and a perforator, which forms perforation lines in said web material in order to divide said web material into single sheets that can be detached along said perforation lines; and said rewinding machine further comprising a weakening device for weakening the web material along a substantially transverse weakening line, along which the web material is severed at an end of winding of a log, said weakening device being arranged to generate said weakening line in a manner synchronized with the end of winding of said log and substantially matching one of said perforation lines.
 28. The rewinding machine as claimed in claim 27, wherein said weakening device comprises an applicator for applying a liquid along said weakening line.
 29. The rewinding machine as claimed in claim 28, wherein said applicator applies water along said weakening line.
 30. The rewinding machine as claimed in claim 28, wherein said applicator applies a liquid containing an adhesive along said weakening line.
 31. The rewinding machine as claimed in claim 27, further comprising a winding core inserter.
 32. The rewinding machine as claimed in claim 31, further comprising a glue applicator for applying glue on said winding cores.
 33. The rewinding machine as claimed in claim 27, wherein said weakening device comprises a rotating element with a liquid dispenser, said rotating element being synchronized with the winding of the log in order to apply said liquid along the weakening line at the end of winding of each log.
 34. The rewinding machine as claimed in claim 33, wherein said rotating element cooperates with a rotating roller supporting the web material, whose peripheral speed is substantially equal to speed of the web material at least during application of the liquid by said liquid dispenser.
 35. The rewinding machine as claimed in claim 33, wherein said applicator is arranged to come into contact with the web material resting on a rotating roller in a manner synchronized with movement of the web material, during the contact a transferring system having a speed substantially equal to the speed of the web material at the contact.
 36. The rewinding machine as claimed in claim 34, wherein said applicator is arranged to come into contact with the web material resting on said rotating roller in a manner synchronized with movement of the web material, during the contact a transferring system having a speed substantially equal to the speed of the web material at the contact.
 37. The rewinding machine as claimed in claim 34, wherein the feed path of said web material develops around said roller, the web material being guided around said roller.
 38. The rewinding machine as claimed in claim 35, wherein the feed path of said web material develops around said roller, the web material being guided around said roller.
 39. The rewinding machine as claimed in claim 34, wherein said rotating roller constitutes one of a plurality of winding rollers forming said winding cradle.
 40. The rewinding machine as claimed in claim 35, wherein the feed path of said web material develops around said rotating roller, the web material being guided around said rotating roller.
 41. The rewinding machine as claimed in claim 37, wherein the feed path of said web material develops around said rotating roller, the web material being guided around said rotating roller.
 42. The rewinding machine as claimed in claim 27, wherein said winding cradle comprises a first winding roller around which said web material is fed and guided, and a second winding roller forming with said first winding roller a nip for transit of winding cores in an initial phase of a winding cycle; and wherein said weakening device is arranged to act upstream of said nip relative to a direction of feed of the web material.
 43. The rewinding machine as claimed in claim 42, further comprising a rolling surface arranged around the first winding roller and upstream of said nip relative to the direction of feed of the web material, defining a channel between said first winding roller and said rolling surface, and wherein said weakening device is arranged to act on the web material upstream of said channel.
 44. The rewinding machine as claimed in claim 43, further comprising a core inserter arranged to feed said winding cores into said channel.
 45. The rewinding machine as claimed in claim 42, wherein said first winding roller has apertures for exit of air therefrom so as to facilitate detachment of a free end of the web material.
 46. The rewinding machine as claimed in claim 39, wherein said one of a plurality of winding rollers has a knurled surface or an engraved surface.
 47. The rewinding machine as claimed in claim 27, further comprising a blowing system to facilitate winding of a first turn of web material around a winding core.
 48. The rewinding machine as claimed in claim 27, further comprising a first glue applicator and a second glue applicator, to apply glue on winding cores in two angularly offset areas, a first area coming into contact with a portion of the web material forming a tail of a complete log and a second area coming into contact with a portion of the web material forming an initial part of a new log of web material.
 49. The rewinding machine as claimed in claim 27, wherein said weakening device comprises a mechanical system or a pneumatic system synchronized with a winding cycle of the logs.
 50. A method for winding rolls of web material around winding cores, comprising: feeding the web material along a feed path; subdividing said web material into single portions that can be detached along transverse perforation lines; winding a quantity of the web material in order to form a first log of web material; when a given quantity of web material has been wound on said log, severing the web material in a severing position along said feed path, forming a tail portion of the first log and a head portion for starting the winding of a second log; starting the winding of said second log; wherein at end of the winding of said log, in a weakening position arranged along the feed path of the web material upstream of the severing position, a weakening line is formed on the web material at one of said transverse perforation lines; the web material is fed along said feed path moving said weakening line towards said severing position; and the web material is severed in said severing position.
 51. The method as claimed in claim 50, further comprising winding said logs around winding cores.
 52. The method as claimed in claim 50, further comprising gluing the head portion of the web material on a winding core at start of the winding of each log.
 53. The method as claimed in claim 50, further comprising weakening said web material by applying a liquid along said weakening line.
 54. The method as claimed in claim 51, further comprising weakening said web material by applying a liquid along said weakening line and wherein said liquid also serves to anchor the head portion of the web material on the winding core.
 55. Rewinding machine for producing logs of web material, comprising a feed path of a web material, a winding cradle, and weakening device; said weakening device comprising an applicator for applying a liquid along a substantially transverse weakening line for weakening the web material along said weakening line, along which the web material is severed at end of winding of a log, said weakening device serving to generate said weakening line in a manner synchronized with the end of winding of said log.
 56. Method for winding rolls of web material around winding cores, comprising: feeding the web material along a feed path; winding a quantity of the web material in order to form a first log of web material; when on said log a given quantity of the web material has been wound, severing the web material in a severing position along said feed path, forming a tail portion of the first log and a head portion for starting winding of a second log; starting the winding of said second log; wherein at end of the winding of said log, in a weakening position arranged along the feed path of the web material upstream of the severing position, a weakening line is formed on the web material by applying a liquid along said weakening line; feeding the web material along said feed path moving said weakening line towards said severing position; and severing the web material in said severing position. 